Lining for digesters



Nrre STATES ARTHUR I): LITTLE, OF PROVIDENCE,

RHODE ISLAND, ASSIGNOR TO JOHN T. IVHEEIBVRIGHT, OF BOSTON, li'IASSAOHUSETTS.

LINING FOR SPECIFICATION rig part of Letters P DIGESTERS.

atent No. 351,330, dated October 19, 1886.

Application filed June 7, 1886. Serial No. 204,371. (No specimens.)

To (all whom it may concern.-

Be it known that I, ARTHURD. LITTLE, of

, Providence, Rhode Island, have invented a new and useful Improvement in Linings for Dig-esters, of which the following is a specification.

My invention relates to wood-pulp digesters madeofcast-iron,inwhichtheso-eallet acid or bisulphite processes are employed, and

10 has still more especial reference to a lining for thesame. Thesedigestersarecommonlylined with sheet-lead, first, to protect the iron of which the shell is made from the corrosive action of acids used or evolved in the manur5 facture of wood pulp by the process named above, and, secondly, to prevent discoloration of the pulp by the salts of iron otherwise formed. In use the lead lining presents cer tain difficulties and objections which it is the object of my invention to remove. Lead expands in heating more than iron, and 011 the cooling down of the digester the lead lining, when in the form of sheets, does not contract sufficiently to return to place, and afterseveral 2 5 operations the lead, especially at its place of fixed connection with the digester side, is thinned out by these alternate expansions and partial contractions, and finally cracks and breaks, no longer insuring the contents from direct contact with the walls of the digester. Owiug'to these peculiarities of the lead linings now in use, constant watchfulness and care are required, and the work of repair is both expensive and tedious. I have found. by experiment that an oxide of lead, as litharge, may be applied to the inner surface of the digester in the form of an enamel or glaze, which will retain all the advantages of the sheet-lead lining in preventing chemical action between 40 the iron walls or shell of the digester and its contents, while at the same time it does not possess the disadvantages of sheet-lead here-l. inabove enumerated. In. carrying out my in vention I employ borate of lead and litharge. Various methods of applying the compound to the digester as a lining will doubtless suggest themselves to builders of digesters, according to circumstances. There are but two principal difficulties to be overcome. First,

the liability of the compound to form bubbles, 5c and, second, the great heat to which the workmen are exposed.

My process has been as follows: Thelitharge and borate of lead are carefully ground and mixed together in the proportions of about ten pounds of the former to one of the latter. The mixed powder is then melted in a pot so constructed that the gas from the tire cannot come in contact with the contents of the pot on account of its reducing action. The pow- 6o der itself is such a poor conductor of heat that I have found it necessary to bring all parts of the melting-pot to a red heat and to stir the mixture constantly. After the mixture is thoroughly melted the pot is removed from the furnace and allowed to stand until the mixture, constantly stirred meanwhile, is free from bubbles, when it is slowly poured into a heavy mold, the bottom of which has the shape of the digester-section that is to be coated. Both the melting and the cooling should be done as quickly as possible to prevent the reduction to lead.

To separate from the mixture any reduced lead formed in the melting, the pot, near its bottom, is provided with a ledge, which keeps back the heavy reduced lead when the melted mixture is poured out into the mold. After the cake which forms in the mold is removed therefrom it is clamped within an iron band, and thus clamped is provided with longhandles by which it may be manipulated, as presently set forth, without exposing the workmen to an unbearable degree of heat. In the meantime the section of the digester which is to be lined is mounted upon slowly-revolving rollers and heated to a red heat by jets of gas mixed withair to burn with a blue flame, the number and size of thejets depending upon the weight of the casting. The cake is now introduced 0 axially through the section to be lined and pressed down by the handles, the workmen standing on either side. This continues until the slowly-revolving casting has melted off from the cake and received auniform coating or lining. Such portions of the edges of the casting as are not affected by the process thus far described are coated by a lump of the In practical use the lining of the digester thus formed works in the same manner as an ordinary lead lining-that is, after a few boilr5 ings there is formed upon either lining a surface coating of sulphate of lead, which, while it is harmless to act upon the wood treated in the digester, protects the glaze of my lining just as it protects the sheet-lead of the ordi-v nary lining.

I claim- A cast-iron digester the inner surface of which is coated with a glaze consisting of oxide of lead and borate or" lead, substantially as described.

vARTHUR D. LITTLE.

\Vitnesses:

W. W. SWAN, XVM. S. ROGERS. 

